1. Field of the Invention
The present invention relates to multiple contact electrical switches and particularly to two-stage starter switches for controlling fluorescent lamps.
2. Description of the Prior Art
Fluorescent lamp starter switches normally are of the two-stage type in which separate ON and OFF buttons control a single pole line switch. The ON button, in addition, controls a momentary contact switch, having separate poles for each lamp being controlled by the switch, to complete the heater filament circuits when starting the lamps. U.S. Pat. Nos. 3,221,112 and No. 3,518,381 issued to Edwin G. Gaynor on Nov. 30, 1965 and June 30, 1970, respectively, disclose two switch designs of that general character. Both of these prior designs have a large number of small precision parts and require a correspondingly large number of hand operations for assembly.
The rocker button style of switch has gained increasing popularity in conventional on-off switching applications in recent years and offers the possibility of permitting a switch to have substantially fewer parts than the previous two-button design. A previous attempt by the present inventor to design a rocker button type of fluorescent lamp switch reduced the number of parts by almost one half; however, prototype switches built to that design did not operate reliably.
Reliability over repeated operating cycles numbering in the hundreds of thousands is a principal requirement for switches that are intended to outlast the useful life of the device on which they are installed. In the case of fluorescent lamp switches, it is particularly important that the transition from "lamp on" to "lamp off" positions be a positive one; that is, the line contacts should not open too soon before the switch button snaps to the "off" position. Otherwise, the operator may fail to latch the switch securely off, and the lamps go out but remain connected to the line.
The initial design referred to above employed a rectangular rocker button loosely positioned in a molded plastic switch case above a contact mounting block, with a metal bezel frame cooperating with side flanges on the button to hold it in place. A pair of integrally molded latching fingers extending from the underside of the button at one end were intended to engage pockets molded in a vertical partition of the mounting block when the one end of the button was depressed to the off position.
Under conditions of actual service, however, the line contacts would open well before the latching fingers were locked in the mating grooves. The operator tended to release the button when the lamp went out and the switch would return to the "on" position. In addition, the plastic fingers would take a permanent set after repeated cycles of operation, and the button would not remain locked even when properly latched by the operator. Also, the loosely positioned rocker button could slide longitudinally in the case, and one end would tend to hang up on the edge of the bezel when the other end was depressed.
Another important aspect in the design of this type of two-stage switch is that it should have the proper "feel"; so that even persons unfamiliar with the switch will quickly learn to distinguish the three positions of momentary "start", "on" and "off". The rocker button of the previous design rested on a transverse row of buttons molded in the top of the contact block. These buttons allowed undesirable longitudinal sliding motion while preventing vertical movement against the contact biasing springs. Again, it was discovered in actual service conditions that this design did not provide the proper sensory cues to enable a person to readily distinguish between operating positions.